Thanks! The main gist of the game is that you can combine your runes, essences and dice (by clicking on them) and then after that you can click on the variables you want to change on the top right!
For example: add (essence) + offense (rune) + d20 (dice) on player attack will increase your attack by how much you roll with a d20. Or, subtract (essence) + offense (rune) + d12 (dice) on an opponent's attack will decrease their attack by how much you roll with a d12 :)